1. Field of the Invention
The present invention relates to an apparatus and method for determining the quantity of material being transported through a passage and, more particularly, to a mass-flow sensor that measures the quantity of reflective bulk material conveyed in an air stream or a non-opaque fluid and a method of using the same.
2. Discussion of the Background
Large quantities of bulk particulate materials such as, for example, agricultural crops, are often transported through ducts, conduits, pipes and the like to an accumulation area for processing or utilization. Often, it is desirable to measure the flow of such material during its transport or the quantity of such material that has been accumulated. Until recently, crop yields have been largely determined on the basis of an entire field, without the ability or the need to obtain information regarding the yields from different locations in a field. Generally, crops were recovered, conveyed to a weighing site and weighed with the transporting vehicle or the container, and the weight of the vehicle or container was subtracted from the gross weight to obtain the amount of product recovered. This process is not dynamic in nature and cannot be adapted to real time collection of data that are necessary for analysis of yields collected from individual field areas.
Systems that can measure crop yields as crops are harvested have previously been used in conjunction with, for example, mobile harvesters. Typically, a mobile harvester simultaneously moves over a field picking crops and stores the picked crops in a receptacle mounted on the harvester. One system involves weighing the crop receptacle and the crops in the receptacle as the harvester moves through the field. Machine dynamics and the large receptacle weight to crop weight ratio, however, lead to serious errors when measurements are made on a real time basis.
A different existing real time measurement system operates by utilizing the fact that certain crops are conveyed to the receptacle by means of an airstream. The airstream is directed in such a manner that the conveyed material impinges on a pressure plate that is connected to a pressure transducer that creates a real time pressure signal indicative of the amount of materials striking the plate. This permits real time determination of the quantity of material that is flowing into the receptacle, with the quantity being proportional to the pressure on the plate. This system is useful because it may be installed on mobile harvesting equipment for the measurement of crop yield as the crops are harvested. This system, however, is not suitable when harvesting certain crops, especially cotton. Cotton and similar crops adhere to the pressure plate, thereby inhibiting the flow of cotton to the receptacle. Additionally, as more cotton accumulates on the pressure plate, inaccurate measurements are taken. Finally, it has been found that the pressure plate system cannot be effectively installed on existing cotton harvesting machinery.
Yet another real time system utilizes optical attenuation of infrared light beams that are projected through the conveying duct. This system requires a combination of emitters and receivers located on opposite sides of the duct. The emitters and receivers must be precisely aligned for the system to work properly. This system, however, is difficult to install. Moreover, this system can suffer from error introduced through stray infrared light, temperature fluctuations and accumulation of material on optical surfaces.
These and other prior art systems, therefore, have several, severe constraints. First, prior art systems are limited in terms of accuracy of measurements. Second, prior art systems are physically complex and difficult to install. Furthermore, residue build-up on sensor surfaces presents a problem with measurement stability in field applications. Specifically, residue builds up on the sensor surfaces, reducing the precision of the measurement of the mass flow and biasing the measurement in favor of higher mass flows over time. Additionally, the prior art considers only overall mass flow and does not take into consideration the various mass components such as, for example, extraneous plant material, that may be present in the flow.
In view of the aforementioned deficiencies attendant with the prior art, it is clear that a need exists for an apparatus and method that can accurately measure the mass flow of conveyed materials without the problems found in prior art systems.
It is an object of the present invention to provide an accurate mass-flow sensor that is simple in design and easy to install.
It is another object of the present invention to provide a mass-flow sensor that is more accurate than previously developed sensors.
It is yet another object of the present invention to provide a mass-flow sensor that can be implemented for the measurement of individual mass components.
It is a further object of the present invention to provide a mass-flow sensor that is capable of physically maintaining clean surfaces on the sensor.
Additionally, it is an object of the present invention to provide a mass-flow sensor that is insensitive to external temperature fluctuation, accumulation of foreign material on operating surfaces and any possible sources of stray light.
To achieve the foregoing and other objects, there is provided a mass-flow sensor for use with a material transport system, e.g., a crop harvester, that overcomes the difficulties found in existing systems. A typical material transport system generally has a conduit defining a flow passage through which entrained materials are transported between inlet and outlet ends of the conduit in a direction parallel to the longitudinal axis of the conduit. The flow sensor comprises a housing unit that includes one or more light sources positioned to project one or more light beams into the flow passage and one or more detectors positioned alongside the one or more light sources to receive light reflected off the entrained materials. The detectors receive the light and convert it into a generated signal indicative of the level of light reflected. A signal processing circuit is connected to the one or more detectors. The signal processing circuit calculates the quantity of material in the flow passage passing through the light beam(s) as a function of the generated signal and a baseline signal indicative of the amount of light measured when no material is flowing through the one or more light beams.
The mass-flow sensor can be used with, for example, a GPS receiver as a cotton yield monitor when mounted on a cotton harvester. It can also be used to measure the mass flow of the various cotton component streams in a cotton gin. These mass flow measurements are made non-intrusively and in real time.
Additionally, the present invention is a method of determining the quantity, or mass flow, of entrained materials flowing through a material transport system having a conduit defining a flow passage through which entrained materials are transported between inlet and outlet ends of the conduit in a direction parallel to the longitudinal axis of the conduit. The method includes projecting one or more light beams through the flow passage in a direction normal to the longitudinal axis of the conduit. The light is detected as it is reflected off the entrained materials flowing through the flow passage. The light is converted into a generated signal indicative of the level of light reflected. The quantity of material in the flow passage passing through the light beam(s) is then calculated as a function of the generated signal and a baseline signal indicative of the amount of light measured when no material is flowing through the one or more light beams.
Further, the present invention relates to a cleaning system for physically cleaning the surfaces of the mass-flow sensor.
With the foregoing and other objects, advantages and features of the invention that will become hereinafter apparent, the nature of the invention may be more clearly understood by reference to the following detailed description of the preferred embodiments of the invention.